Analyzing attempt and success factors for amputated digit replantation in Japan using the diagnosis procedure combination database

The number of amputated finger replantation has declined in the USA and Germany in recent years; however, there have been no reports on recent trends in Japan. We examined the current practices, attempts, and success factors of digit replantation in Japan. We hypothesized that the rates of digit replantation and success rates were consistently standardized in Japan. The diagnosis procedure combination database was used to analyze 14004 cases from April 2014 to March 2020, excluding multiple-digit amputations, thus focusing on 13484 patients. We evaluated replantation success rates and identified factors influencing replantation decisions using multiple logistic regression analysis. The key findings included a higher frequency of replantation in thumb cases and surgeries during overtime hours, on Sundays, and in educational institutions. Success rates were notably higher for thumb replantations and patients under 20 years of age. Patients over 65 years of age treated with urokinase showed higher failure rates, unrelated to regional or hospital case volumes. The number of amputated digit replantation surgeries in Japan was high during overtime hours, on Sundays, and in educational institutions. Region, hospital type, and hospital case volume were not associated with a low success rate across Japan.


Data collection
Patient data labeled with codes S680 (thumb amputation), S681 (amputation of digits other than the thumb), and S682 (multiple-digit amputation), based on the International Classification of Diseases 10th revision, were extracted from the DPC database.Patients with multiple-digit amputations were excluded from the logistic regression analysis of replantation rates.Moreover, cases of devascularization (S654, S655) were excluded to ensure uniformity of severity.The success and failure rates are described below.A total of 13484 patients were enrolled in this study.Epidemiological data on reimplanted amputated digits were collected, including the injured digit, patient's age, day of the week on which surgery was performed, and whether it was an overtimehour operation.

Factor setting
The factors that influenced the decision to perform replantation in cases of digit amputation were identified.These factors included age, injured digit, comorbidities at admission (such as diabetes, heart failure, and cerebrovascular accidents), day of the week on which surgery was performed, operation start time, and hospital classification (educational or non-educational institution).We also investigated factors associated with success/ failure after digit replantation, hospital case volume, and type of intravenous anticoagulation used (prostaglandin E1, heparinoid, and urokinase).The rate of attempted replantation was defined as the percentage of patients who underwent replantation surgery for amputated digits.With reference to previous reports, failure was defined as cases in which a patient had undergone flap surgery, amputation, free flap transfer, wound treatment, or local negative pressure closure procedures within 2 weeks after digit replantation surgery during the same hospitalization period 4,12,14,15 .Multiple-digit amputation cases were excluded from the logistic regression analysis owing to the difficulty in calculating the failure rate when including them.

Statistical analysis
Factors influencing the decision to perform replantation for amputated digits and those influencing success/ failure after replantation were analyzed using logistic regression analysis with adjusted models.All calculations were conducted using STATA ver.16.1 (Stata, College Station, TX, USA).Significance was set at P < 0.05 for all analyses.Data are presented as mean ± standard deviation or as odds ratios (ORs) with 95% confidence intervals (CIs), unless otherwise stated.

Conference presentation
Oral presentation in part at the 12th Congress of the World Society for Reconstructive Microsurgery, in Singapore, August 17 through 19, 2023.

Replantation surgery rates after digit amputation
Replantation was performed in 1,786 (13.2%) of the 13,484 patients.There was a significantly higher rate of patients aged < 19 years (OR 1.25; 95% CI  www.nature.com/scientificreports/ of replantation for thumb amputation and the similarly high frequency of replantation in younger patients were consistent with those in previous studies 16.These data provide a comprehensive overview of digit replantation in Japan.The higher rate of attempted replantation in elderly patients was unexpected with respect to the replantation rates.It is possible that patients aged 65 years or older were more willing to undergo replantation (even if the treatment time was long) than the working-age group, aged 20-64 years, who sought to return to work as soon as possible after injury.This is the first study to show that finger replantation is more frequently selected in surgeries for finger amputations beyond normal working hours, such as on Sundays and after work hours.
This study also showed that the replantation rate was high in educational institutions, which was comparable to previous reports 12,15 .Cho et al. reported that replantation was 2.4 times more common in educational hospitals located in urban centers than in other areas 12 .As 36.5% of digit amputation cases were replanted in educational hospitals and the failure rate was comparable to that in non-educational hospitals, educational hospitals may play an important role in digit amputation cases.
The success rate of replantation was 84.9% in 2013 14 , while it was 83.4% in 2018 12 .The success rate of replantation in this study was 90.54%, which is comparable with or better than previous results [17][18][19] .Age affects the failure rate after replantation 17,18 .The present study corroborated this finding by revealing a higher failure rate in patients over 65 years of age.Hospitals with a larger number of cases have lower failure rates after replantation 20 .However, the number of cases at each hospital had no effect on the success rate in this study.Furthermore, the success rate of replantation techniques was higher in the Kinki region than in other regions of the country.A possible reason for the better results in this area than in other areas is the presence of a facility with which Komatsu and Tamai were affiliated.However, this study indicated that the hospital case volume does not affect the success rate of replantation in Japan.These results indicate that replantation for amputated digits is performed in Japan without regional differences, and that the failure rate in all regions is comparable to that in other countries.
Although the rate of replantation was higher among patients with diabetes, the postoperative failure rate was comparable to that among patients without diabetes.We considered that patients with diabetes have a higher rate of reimplantation because of the higher prevalence of diabetes in the elderly population.Our finding that diabetes is not associated with postoperative failure also has implications for surgical indications.Furthermore, antithrombotic therapy after replantation is widely used, and its effectiveness is based on data from studies in rat models 21,22 .Many negative reports exist on the efficacy of antithrombotic therapy after replantation.In this study, the use of heparinoids and PGE1 did not affect the postoperative failure rate 23,24 .However, this study showed that urokinase use was significantly correlated with failure, and it is possible that patients who receive antithrombotic therapy may be severely injured at the time of injury.In fact, urokinase was used in only 6.5% of all cases, and its use may have been preferred in cases with a high probability of failure.Therefore, the risk of failure was not increased by the use of urokinase, but rather reflected the initial severity of the disease.
This study had several limitations.It was a retrospective observational study based on DPC data; therefore, the surgical details are unknown.Second, this study was limited to cases involving hospitals participating in the DPC.Therefore, it does not reflect the results of other institutions.Third, the detailed amputation levels and injury status at the time of amputation were unknown; therefore, this study did not standardize the cases.In particular, the amputation level and injury status are reported to affect the success rate after replantation of amputated digits 25 .However, these data are not standardized and may not reflect the appropriate postoperative outcomes.A further consideration is the definition of failure rate.We defined failure as a case in which the patient underwent reoperation during the same hospitalization within 2 weeks of the initial surgery.Because we could not obtain data on cases in which the patient was readmitted to the hospital and underwent surgery after being discharge, it is possible that we may have underestimated the number of failed cases.Therefore, we were unable to completely capture the actual status of case success/failure.
In the future, standardizing the treatment of amputated digits will be necessary by compiling a database of cases, including the amputation site and the degree of injury.This information will lead to stricter indications for the replantation of amputated digits that should increase the success rate of surgery.

Conclusion
In Japan, replantation is frequently performed for amputations in young and older adult patients, on the thumbs, in the after hours, on Sundays, and in educational institutions.The success rate is higher for the thumb and lower for older patients and patients using urokinase.Region, hospital type, and hospital case volume were not associated with a low success rate across Japan.